Reloj Mundial

A live dashboard of "what time is it right now" everywhere

This world clock shows the current time in several cities at once and keeps every clock ticking in real time, updating once per second. It is built for the everyday question "is it a reasonable hour to message my colleague in Tokyo right now?" — a glance, not a calculation. It starts with six common zones (UTC, New York, London, Tokyo, Sydney, Los Angeles), and you can add any city from the full list your browser knows about. Each card displays the live time, the date, the UTC offset, and a sun or moon icon indicating whether it is currently day or night there.

How the live clocks stay correct

Every second the tool reads your device's clock and re-renders each card by formatting that single instant in each city's timezone. It uses the JavaScript Intl API and the IANA timezone database bundled in your browser, so the offsets it shows already account for daylight saving time on today's date. That is why the UTC offset on a card can change on the day a region shifts its clocks — the tool is not storing a fixed number, it is asking the timezone database fresh each tick. The list of selectable zones comes from Intl.supportedValuesOf('timeZone'), which on a modern browser is the complete set of several hundred IANA zone identifiers.

The day/night indicator

Each card shows a sun (☀️) between 6:00 and 17:59 local time and a moon (🌙) otherwise. This is a deliberately simple rule — a fixed 6 AM to 6 PM "daytime" window — so it is an approximation, not an astronomical sunrise/sunset calculation. In high latitudes during summer or winter the real daylight hours stretch well beyond that window, so treat the icon as a quick "are they likely awake?" cue rather than a literal sunlight reading.

A worked example

Suppose it is 15:00 in London in July. The London card reads 15:00 with a sun and an offset of UTC+01:00 (British Summer Time, not +00:00, because the tool resolves DST live). The New York card reads 10:00 with a sun and UTC−04:00. The Tokyo card reads 23:00 with a moon and UTC+09:00 — instantly telling you that pinging a Tokyo colleague right now means waking them up. Add Sydney and you would see the next calendar day already begun there. All of this without entering a single time: the dashboard simply reflects "now" everywhere.

Useful features

• 24-hour / 12-hour toggle. Switch between 23:00 and 11:00 PM formatting to match your preference; it applies to every card at once.
• Add any zone. Use the dropdown to add a city; the card appears immediately and starts ticking. The default six cannot be removed, but cities you add can.
• UTC offset shown on every card, including half-hour and 45-minute offsets (India at UTC+05:30, Nepal at UTC+05:45), which are easy to forget when doing the math in your head.

When to use a world clock versus a converter

A world clock answers "what time is it now in these places?" — it is a passive, always-current display. If instead you need to plan a specific future moment ("if we meet at 9 AM my time next Tuesday, what time is that for everyone?"), that is a scheduling task better suited to a timezone converter, where you set an arbitrary date and time as the reference. Use this world clock for the ambient, ongoing awareness of remote teams, family abroad, or markets; use a converter when you are pinning down one event.

Tips and pitfalls

• It trusts your device's clock. Every time shown is derived from your computer's current time, so if your machine's clock or its own timezone is wrong, every card is off by the same amount. Confirm your system time is accurate.
• The day/night icon is approximate. Near the poles, or for anyone working unusual hours, the 6-to-6 rule will not match reality. It is a hint, not a guarantee that someone is asleep.
• Added cities reset on reload. The list of clocks is held in memory for the session, so refreshing the page returns to the default six. Re-add your regular cities as needed.
• Keep your browser updated. Because DST rules come from the database shipped with your browser and OS, occasional government changes to those rules are only reflected once you update.

The clock runs entirely in your browser using the bundled timezone data — no location, clock, or list of cities is sent anywhere.